One type of aerosol dispensing container has a collapsible bag or pouch-like structure disposed within the container. The interior of the bag defines a product chamber for holding a product to be dispensed. A propellant chamber for holding a pressurized propellant is formed between the interior of the container and the exterior of the bag. The bag has an opening for communicating with the exterior of the container and a dispensing means, typically a valve, for sealing the product chamber and for selectively dispensing the product. The propellant exerts a compressive force on the bag, collapsing the bag and forcing the product to be dispensed from the container as the valve is actuated. Thus, the product is not contaminated by the propellant and the propellant is not vented to the atmosphere.
One type of dispensing container that will be referred to as "insertion container" requires an assembly method which will be referred to as the "insertion method." The insertion method requires assembly of a cylindrical side body, top and bottom closures and a special type of plastic bag which is adapted to be inserted into a valve opening, typically about one inch in diameter, in the top closure. Since the "insertable" bag must be able to fit through the relatively small valve opening, it must be specially constructed to permit it to be folded and/or steamed or otherwise collapsed to increase the bag's flexibility, while still maintaining its integrity during subsequent processing steps including exposure to the pressurized propellant.
The insertable bag and the insertion method have several additional disadvantages. Not only is the assembly process relatively slow, cumbersome and expensive due to the special steps required to prepare the bag for insertion through the valve opening but they may also produce non-uniform surfaces and cracks, especially around the bag opening, resulting in poor sealing characteristics at the valve opening/bag interface which permit propellant and/or product leakage or permeation out of the container. This increases with the age of the unfilled bag. Attempts to utilize a gasket or adhesive to seal the interface have not been entirely successful and also increases manufacturing costs and crimp leakage problems. Furthermore, since the bag is typically made of a relatively thin plastic to enhance its flexibility, the propellant pressure tends to collapse the middle of the bag and trap product at the bottom of the bag.
In one type of filling operation, the insertable bag may be filled atmospherically through a bag opening prior to a valve cup being attached to seal the valve opening and pressurization of the propellant chamber. Unfortunately, this type of filling operation may result in trapped air in the product chamber. It also requires expensive refrigeration filling for post-foaming products that expand or foam at normal room temperatures. In another type of filling operation, the valve cup is first crimped to the valve opening, the product chamber is evacuated to remove any trapped air, the propellant chamber is pressurized and then the product chamber is filled through a nozzle in the valve cup.
In order to prevent collapse of the middle portion of the insertable bag, another type of container that will be referred to as a "pleated bag container" was developed. The pleated bag container utilizes a non-cylindrical bag having a plurality of pleats or folds disposed along the longitudinal axis of the bag. The pleats collapse in an accordion-like manner along the longitudinal axis in response to the internal propellant pressure while preventing the radial collapse of the middle portion of the bag. The pleated bag, however, can not be inserted into the valve opening and must be inserted into the container before the top closure is attached to the can body. After the top closure is attached to the container body, the bag is positioned so that a neck portion of the bag rests on the valve opening, the upper portion of the bag is cut forming a vertical flange which is heat formed to the valve opening, and the flange is sealed between the valve cup and the top closure seal. The bag may be filled atmospherically through the bag opening prior to the attachment of the valve cup to the body. Alternatively, the bag may be loaded with product after the bag is evacuated and the propellant chamber pressurized.
Unfortunately, the pleated bag container has several disadvantages. The pleated bag is relatively difficult and expensive to manufacture. The pleated configuration of the bag may also lead to fracture or failure due to the rapid contraction/expansion of the bag as the bag is first evacuated and then forced filled. Further, the pleated configuration has significantly more surface area than the non-pleated bag which requires more plastic and increases permeation of the propellant through the increased surface area. Although the pleats prevent full collapse of the bag, they also decrease the capacity of the bag and prevent full evacuation of product from the bag resulting in greater product loss.